1. Field of the Invention
This invention relates generally to the access of digital data from optical storage media by a personal computer. Optical storage methods allow information to be recorded and recovered from a given material by using light. The compact disk (CD) media currently used in optical recording is capable of significantly higher areal density than magnetic disks. This capacity to store a large amount of information per unit area of the media surface is a major advantage of CD technology over magnetic disk storage techniques.
2. Prior Art
The field reliability of CD systems is yet to be determined due to the relatively short period of time this media has been in use. However, optical recording systems are expected to be more reliable than magnetic disk drives, generally referred to as hard disks, for several reasons. The optical heads used for recording and recovering information are spaced away from the disk at all times, eliminating the possibility of head crashes. And the optical techniques used cause no wear or tear on the media surface during reading or transferring of information.
The reliability characteristic of optical storage media appears to be especially advantageous where the removability and transportability of the media is critical. Compared to magnetic disk drives, both hard and floppy, the operation of a CD is much less sensitive or affected by dust accumulation on either the head or the media. And the optical methods of reading and writing data without making physical contact with the media surface significantly reduces the potential for damage in removable disk applications.
The integration of CD drives into personal computers comprises one of the largest markets for optical storage media applications for the foreseeable future. At present, the cost of a CD drive is a primary barrier to the growth of this market. However, the CD-ROM (read only memory) standard as originally developed by Sony and Phillips has become the standard defining the physical characteristics and disk format for data storage and retrieval. This format has become very popular for making large amounts of information available to users at a relatively low cost and there is an increasingly large library of CD-ROM titles available. CD drives which are capable of writing information to the CD are much less widely used today due to their much greater cost and complexity.
All CD drive designs include a CD load mechanism, a spindle, drive electronics and a controller. The drive electronics recovers data from the CD as directed by the controller. The controller manages the flow of commands, status flags and data between the host personal computer and the CD drive electronics.
Conventional CD drive designs support the Industry Standard Architecture (ISA) bus convention and require the insertion of an interface card or host adapter card into an ISA input/output bus slot of the host personal computer. These disk drive designs include a variety of proprietary and manufacturer specific designs as well as designs that support the three varying software driver formats used with the Small Computer Systems Interface (SCSI) standard. These three software driver formats include Microsoft's Layered Device Driver Architecture, the American National Standards Institutes' Common Access Method, and the Advanced SCSI Programming Interface.
A SCSI disk drive includes a controller and a SCSI slave interface. A SCSI disk drive communicates with a host computer through a SCSI host adapter card which must be resident on the ISA bus of the host. There are three types of host adapter cards, namely a register compatible controller, an INT 13 h compatible controller, and an installable device driver. These types of host adapter designs are fully explained in widely available technical publications.
The reliance of all conventional CD drive designs exclusively on the use of the ISA input/output bus results in the additional expense of host adapter card electronics. Furthermore, a reduction in the range of employment of any given computer system due to the permanent commitment of an input/output bus slot to communication with the CD drive controller is a limitation in the prior art.
An alternative bus structure is available within standard personal computer architecture available for use with a CD drive controller. This structure is referred to as integrated drive electronics with an AT attachment interface, or IDE/ATA. The American National Standards Institute has published this standard and it is currently widely available. The term integrated drive electronics includes any drive with a controller included. For example, all SCSI drives are in fact IDE drives. The term IDE/ATA applies to a drive if and only if its interface conforms to the industry standard AT attachment specification. IDE/ATA drives do not take up an ISA input/output slot. This class of interface is connected by means of a dedicated 40 pin connector found on many personal computer mother boards.
Conventional CD drives in the prior art failed to make use of the IDE/ATA bus. However, now that the AT standard has become widely used in many personal computers, it would be desirable to provide a CD drive with built-in controller functionality and a standard connector. This would obviate the need for an additional host adapter card and associated electronics. Providing these electronics in addition to the CD drive itself increases the overall cost of a system using a CD drive for data storage and retrieval and also makes a CD drive more complicated to install on existing personal computers in use today. Due to the plethora of methods of ISA interface designs used in the industry today, compatibility issues often occur when, for example, a particular CD drive controller is tasked with communicating with another ISA bus connected peripheral device. The high frequency of incompatibility often prohibits the employment of the most cost efficient or highest performance combination of devices. The present invention, a controller for CD drives which can be implemented with a drive using a standard AT connector, overcomes the problems associated with the prior art as will be made clear in the following discussions thereof.